A seesaw is an example of a first class lever The fulcrum, which is the part of the lever that does not move, is in the middle. The resistance, which is the weight (person) you are trying to lift is at one end. The effort, which is the force applied to the lever, is the person sitting on the other end.
Stimulant speeds up body functions but depresses brain activity
Inhalant dissolves the fatty tissue in the brain
Steroids influences moods in the limbus system
Bone marrow, is one but I don't know any else off the top of my head
